X-ray tube



X-RAY TUBE Filed June 9, 1925 Inventor Patented June 11, 1929.

UNITED STATES PATENT OFFICE.

ALBERT nouwnns, or EINDHOVEN, NETHERLANDS, AssIG'N'oR TO, N. v. PHILIPS GLOEILAMBENEABRIEKEN, or nmnnovnn, NETHERLANDS. I

X-RAY T BE.

Application filed June 9, 1925, Serial No. 35,930, ,and in the Netherlands July 23, 1924.

This invention relates to X-ray tubes, more particularly to X-ray tubes in which the active portion of the anticathode is made of tungsten. WVhen using X-ray tubes for radiographic purposes, great energy is as a rule concentrated for a very short time on a small portion of the anticathode, but also in X-ray tubes for therapeutic purposes great energy is frequently supplied to the anticathode. Many means for carrying off this energy have been proposed which may be based on heat conduction or on heat radiation. In spite of these means it occurs, however, that the energy supplied to the anticathode cannot be carried off so quickly that the anticathode is prevented from disintegrating.

An object of the invention is to provide a' construction of an Xray tube in which much energy can be carried off from a very small focal spot. Another object of the invention is to diminish the risk of disintegration of the anticathode. A further object of the invention is to provide an X-ray tube showing a very effective cooling of the active surface of the anticathode.

According to this invention the tungsten anticathode of an X-ray tube of the incandescent cathode type is hollowed at the place of the focal spot. The focal spot in such an X-ray tube being consequently located in a cavity of the anticathode, the cooling is much more effective than in X-ray tubes having a plane anticathode, for in X-ray tubes according to the invention the ratio of the surface of the anticathode portion struck by the cathode-rays and the section of the beam of X-rays leaving the anticathode will be greater than it is in X-ray tubes having a plane anticathode. In X-ray tubes having a. plan-e anticathode the surface of which forms an angle of with the direction of the X-ray beam, the ratio of the surface of the focal spot and the section of the leaving beam of X-rays is about 2 whereas r in X-ray tubes according to the invention comprising an anticathode with a cavity having the form of a cone the solid angle of which is for example 30, the ratio of the surface of the focal spot and the section of the beam of X-rays leaving the anticathode in the direction of the axis of the cone, will be about 4.2. For that. reason, too, the cooling of the anticathode at a given sharpness of image will be more intensive than an X-ray tube in Which-the active portion of the anticathode forms a plane. d

An additional advantage of X-ray tubes according to the invention exists in that in the cavity of the anticathode there is a space nearly free from any electric field. In X-ray tubes as hitherto known it often occurs that the strong field between the cathode and the anticathode draws tungsten particles off'the incandescent anticathode, which,on the contrary in X-ray tubes according to the invention owing to the presence of said space nearly free from any electric field, occurs to a less extent so that also on that account the possibility of the anticathode being damaged is diminished.

The invention will be more clearly understood with reference to the accompanying drawing, representing an embodiment of the invention. An incandescent cathode 2 is fiXed in a metal vessel 1 to the wall of which is secured a metal cover 3 having an aperture in front of which stretches part of the surface of an anticathode 4. In known arrangements the anticathode of an X-raytube is provided with a tungsten target mounted in a copper body. The anticathodeof the tube illustrated which on the outsidemay consist for example, of chrome-iron, comode X-ray tubes hitherto known in that the tungsten body 5 has a hollow conical face. In the metal vessel opposite the anticathode is a window for the passage of the X-rays generated. This window consists of a glass hood 7 which is hermetically sealed to the metal wall, an annular metal plate 8, for example, of iron being provided for screening the X-rays and for preventing the Weld 9 from being struck by cathode rays. One leading-in wire 10 for the incandescent cathode passes insulatingly through the metal ring 8 and is sealed into the glass hood 7 the other leading-in wire is formed by the conductive connection of the pole 11 with the metal ring 8 and the metal :nvelope 1. The X-ray tube is either highly evacuted or has a gaseous filling of hydrogen or helium hav-' ing a pressure above 0.0006 millimetre of mercury which is such that any gas ionization can be obtained.

That I claim is: 1. An X-ray tube comprising an incandes- 15 cent filament cathode and an anticathode consisting partly of tungsten, the anticathode being hollowed at the place of the focal spot.

2. An X-ray tube comprising an incandescent filament cathode and ananticathode pro- Vided With a hollow cone-shaped insert of tungsten at the place of the focal spot.

3. An X-ray tube comprising an incandescent cathode and an anticathode provided With a cone-shaped insert of tungsten of approximately uniform thickness at the place of the focal spot.

In testimony whereof I affix my signature, at the city of Eindhoven, this 20th day of May, A. D. 1925. I v

ALBERT BOUWERS. 

